Figure 2. Flow characterization.

After collagen hydrogel polymerization, green fluorescent beads were suspended in PBS and perfused through the left lateral microchannel. (A,B) When low volumes (10 μl) were injected, the flow profile observed was completely parallel to the hydrogel and no sphere penetration into the hydrogel was observed. (C,D) When large volumes (300 μl) were injected, an interstitial flow through the hydrogel was observed, showing sphere penetration into the hydrogel. Scale bar is 400 μm. (E) Parallel and interstitial flow are determined by the indicated parameters, where “R_hydrogel” is the flow resistance generated by the hydrogel, and “R_channel” is the flow resistance through the lateral microchannels.